It is known to provide overflow sieves, more particularly arcuate sieves, as a slotted sieve consisting of individual bars which are substantially triangular in cross section and which are welded in spaced parallel relationship onto a supporting construction so that the bars form between themselves narrower or wider gaps, depending on the mixture of solids and liquids to be sieved. Such slotted sieves are expensive to construct and assemble and must be changed together with the supporting construction during replacement. Furthermore, they can be adapted only to a limited extent to the various textures of the material to be sieved.